Don't use LibGetVariable(), since it doesn't give us real error codes.
Make vendor_cert/vendor_dbx actually replaceable by an external tool.

This moves them both to be computed at runtime from a pointer+offset
rather than just a pointer, so that their real address can be entirely
derived from the section they're in.

This means you can replace the whole .vendor_cert section with a new one
with certs that don't have the same size.
Harden shim against non-participating bootloaders.

It works like this: during startup of shim, we hook into the system's
ExitBootServices() and StartImage().  If the system's StartImage() is
called, we automatically unhook, because we're chainloading to something
the system can verify.

When shim's verify is called, we record what kind of certificate the
image was verified against.  If the call /succeeds/, we remove our
hooks.

If ExitBootServices() is called, we check how the bootloader verified
whatever it is loading.  If it was verified by its hash, we unhook
everything and call the system's EBS().  If it was verified by
certificate, we check if it has called shim_verify().  If it has, we
unhook everything and call the system's EBS()

If the bootloader has not verified anything, and is itself verified by
a certificate, we display a security violation warning and halt the
machine.
Include shim's vendor_cert in MokListRT

There needs to be some way to communicate to the kernel that it's a
trusted key, and since this mechanism already exists, it's by far the
easiest.
MokManager needs to disable the graphics console.

Without this patch, on some machines we never see MokManager's UI.  This
protocol has never (I think?) been officially published, and yet I still
have new hardware that needs it.

If you're looking for a reference, look at:

EdkCompatibilityPkg/Foundation/Protocol/ConsoleControl/ConsoleControl.c

in the edk2 tree from Tiano.

Signed-off-by: Peter Jones <pjones@redhat.com>